Scanning probe microscopy (SPM) is a relatively new form of microscopy that is used to image surfaces and small objects that are supported by surfaces. Scanning probe microscopes (SPMs) use a very small probe, frequently a sharp tip that may be attached to a cantilever, to gather information about surfaces and small objects. This probe is scanned laterally, very close to the surface or objects, while interactions between the probe and surface or objects are measured. The “images” formed by SPMs are plots of the measured value of these interactions as a function of position along the surface or object. In a generalized sense, scanning electron microscopes (SEMs) and scanning transmission electron microscopes (STEMs) can also be considered as being part of the SPM type family of microscopes where the scanning probe is a fine beam of electrons.
SPMs are categorized by the type(s) of interaction that they measure and plot. The two most common types of SPMs are the scanning tunneling microscope (STM) and the atomic force microscope (AFM). STMs measure tunneling currents between the probe and surface. AFMs, in contrast, measure quantum-physical forces between the probe and surface or object. Exemplary forms of scanning probe microscopy are listed in the following table:
AcronymNameAFMatomic force microscopyEFMelectrostatic force microscopeESTMelectrochemical scanning tunneling microscopeFMMforce modulation microscopyKPFMKelvin probe force microscopyMFMmagnetic force microscopyMRFMmagnetic resonance force microscopyNSOMnear-field scanning optical microscopyPFMpiezo force microscopyPSTMphoton scanning tunneling microscopyPTMSphotothermal microspectroscopy/microscopySECMscanning electrochemical microscopySCMscanning capacitance microscopySGMscanning gate microscopySICMscanning ion-conductance microscopySNOMscanning near-field optical microscopy (same as NSOM)SPSMspin polarized scanning tunneling microscopySThMscanning thermal microscopySTMscanning tunneling microscopySPSTMspin-polarized scanning tunneling microscopySVMscanning voltage microscopySHPMscanning Hall probe microscopyCDSPMcritical dimension scanning probe microscopeSEMscanning electron microscopeSTEMscanning transmission electron microscopeCertain types of SPMs can be used to image surfaces or objects at atomic resolution. In principle, SPMs can resolve individual atoms, groups of atoms, molecules, and arrays of molecules (at a fraction of the nanometer length scale). However, the accuracy of the performance of SPMs is limited by the accuracy of the two-dimensional (2D) scanning mechanism (i.e., the accuracy with which two-dimensional positions along the surface can be controlled and measured), among other limitations such as the finite size of the SPM probe tip. Thus, there is a need for improved systems for assessing the performance, calibrating, and enhancing SPMs.